Effect of Quadrat and Core Sizes on Determining the Spatial Pattern of Criconemella sphaerocephalus

Abstract

An unmanaged pasture was sampled on four occasions (A, B, C, D) with five different quadrat sizes for Criconemella sphaerocephalus by removing a constant soil core volume of 75 cm³ (A) and 300 cm³ (C) from increasing quadrat areas of 0.5-8 m², and removing soil core volumes of increasing size - 75-1,200 cm³ (B) and 300-4,800 cm³ (D) - proportionally with an increase in quadrat area (0.5-8 m²). Frequency counts of C. sphaerocephalus were fitted to six probability distributions. The index of aggregation (b) for Taylor's power law and Morisita's index of dispersion were also calculated where appropriate. Twelve of nineteen of the sampling combinations were best described by negative binomial distribution (P = 0.05). Criconemella sphaerocephalus appeared more highly aggregated when sampled with constant soil core volumes (A and C) than from increasing soil core volumes (B and D) based on Taylor's index of aggregation (b). Morisita's index of dispersion indicated aggregation at the smallest quadrat area (0.5 m²) for all sampling occasions (A, B, C, D). Key words: spatial distribution, Taylor's power law, Morisita's index of dispersion, Criconemella sphaerocephalus.